The present invention relates generally to an alternator brush holder assembly and, more particularly, to improved reliability for a spring type brush assembly.
Dynamo electric machines such as generators, motors, and automotive alternators may include brushes that provide electrical communication between a spinning rotor and other components of an electric machine circuit. Brushes are typically composed of carbon and graphite materials. When part of a rotor circuit, the brushes may be contained in a brush holder assembly that include springs which cause the brushes to maintain firm contact with electrically conductive rotating portions of a rotor. In a typical alternator, two slips rings are located on one end of the rotor assembly and are respectively connected to opposite ends of the rotor field winding. The corresponding pair of brushes is typically positioned to be urged by the springs against the rotating slip rings.
The rotor of an automotive alternator is typically driven by a belt and pulley system to rotate within stator windings coiled on a laminated iron frame. The magnetic field from the spinning rotor induces an alternating current into the stator windings. The alternating current (AC) voltage is typically then converted to a direct current (DC) voltage by diode rectifiers that output the DC voltage to one or more batteries and to electrical devices of a vehicle. Associated apparatus may include a regulator and a controller for, among other things, monitoring battery voltage and current going to the field winding of the rotor. The DC output voltage may be, for example, 14 volts, which is generally at least one volt more than a conventional vehicle's battery voltage, for example 12.7 volts. The field winding current for conventional automobile alternators may be as much as 5-8 amps, and ambulances, buses, semi-tractors and various vehicles may require more current, for example, for powering air-conditioning, heaters, lights, refrigeration units, etc. while a vehicle is idling.
Electrical communication between an electricity source and a brush may be provided by a braided or twisted wire having one end connected to the brush and the other end connected to the electrical source via one or more electrical terminals. Such wire is often termed a shunt or shunt wire by those skilled in the art. Some conventional brushes have a shunt wire protruding from the rear of the brush through the center of a spring. This can be problematic because the shunt can tangle with the spring when the brush spring is compressed. A tangled shunt may cause the brush to become stuck, resulting in removal of field current from the alternator. In such a case, no electrical output is produced by the alternator. Other conventional brushes have a shunt protruding from the top/bottom of the brush. However, with a non-symmetrical brush, such as a brush having an angled front contacting surface, this configuration is undesirable because the negative and positive brushes are required to be different parts. For example, the shunt may protrude from the top of a negative brush and from the bottom of a positive brush.